U.S. patent application Ser. No. 13/175,681 (“the '681 patent application”), filed Jul. 1, 2011, entitled, “Overlay System With Digital Optical Transmitter For Digitized Narrowcast Signals,” which is incorporated herein by reference in its entirety, discloses various implementations of improved cable-based overlay systems used to deliver high-definition digital entertainment and telecommunications such as video, voice, and high-speed Internet services from a headend to subscribers.
The implementations of the improved overlay system disclosed in the '681 patent application operate to combine a digitally transported digitized narrowcast transmission with a broadcast transmission that is amplitude-modulated and transported on an analog optical link on a separate, dedicated fiber. Separate transport mechanisms for broadcast and narrowcast transmissions creates a need for more network resources and also results in a less than optimal use of a network system's bandwidth capabilities. Therefore, a need exists for improving methods and systems for delivering narrowcast and broadcast transmissions to a subscriber.
In general, a large amount of information is broadcast to an entire group of subscribers, and a relatively small fraction of information is narrowcast to small sub-groups of subscribers, wherein each sub-group (e.g., represented by a node or node port) receives narrowcast information that is unique to the sub-group. Typically, the delivery of a unique narrowcast transmission to a sub-group requires a narrowcast transmitter and an optical wavelength that is dedicated to the sub-group, and dedicated to said sub-group alone. For example, current optical architectures require at least one narrowcast transmitter and one optical wavelength per sub-group (e.g., node or node port). Therefore, a need exists for creating greater efficiency in the use of narrowcast transmitters and for allowing a narrowcast transmitter and an optical wavelength to serve more than one node or node port.
Typically, a CMTS transforms a signal into the time domain (e.g., using an inverse fast Fourier transform (IFFT)) before outputting the signal to a transmitter. The transformed signal is then transported to a transmitter and then output to a receiver. Transporting, re-transforming, and compressing data received from the CMTS requires a large amount of network and network component resources. Therefore, a need exists for improving the transport of data from a CMTS to a downstream component.
Generally, optical networks do not provide independent control or adaptation to individual channel amplitude and performance characteristics. This lack of control and resulting insufficient margins in forward and return traffic along the optical networks, can lead to the need for reserving large amounts of headroom to account for worst-case scenarios. Remote PHY (physical layer) architectures typically attempt to resolve the headroom issue by placing modulation and demodulation remotely at nodes. However, placing modulation and demodulation at nodes comes at the expense of a loss in transparency and of incompatibility with existing RF system components. Therefore, a need exists for improving forward and reverse transmissions through an optical fiber system.
Typically, return link transmitters are designed for a specific noise-to-power ratio (NPR) (e.g., 40 dB NPR) in a significant dynamic window (e.g., 15 dB dynamic window) to account for set up issues and to provide immunity from ingress clipping events. In embodiments, data inputs can be compressed such that NPR is maintained within a link capacity and within an associated dynamic window. For example, broadband companding is a lossy compression method that can be applied to limit bitrates in return transmitters. In embodiments, when ingress is present or when one or more channels are relatively strong compared to others, the noise of the companding process impacts the other channels (e.g., the weaker channels) and achievable modulation error ratio (MER) for the other channels is reduced. In practice, the 40 dB NPR is generally unavailable for weaker channels in the presence of strong channels when all are residing within the proper radio frequency (RF) level set-up window. Therefore, a need exists for improved data compression to support combining and transporting broadband compressed forward (BCF) and remote physical layer (R-PHY) channels.
Like reference numbers and designations in the various drawings indicate like elements.